Thermosetting powder coating composition

ABSTRACT

To provide the thermosetting powder coating composition which comprises a fluorine-containing copolymer having crosslinkable functional group and a curing agent, in which the fluorine-containing copolymer has a fluoroolefin unit, has a fluorine content of not less than 10% by weight and is not dissolved in tetrahydrofuran substantially. A coating line can be shared with other powder coating composition because even when the composition mixes to other powder coating composition, it causes no coating defects, and yet a coated article having a coating film excellent in physical properties can be provided.

TECHNICAL FIELD

The present invention relates to a thermosetting powder coatingcomposition. Particularly the present invention relates to athermosetting powder coating composition which is less affected bymixing of other powder coating composition at coating.

BACKGROUND ART

Powder coating compositions containing a fluorine-containing resin areknown in various patent publications such as JP -B-6-104792,JP-A-1-103670 and JP-A-8-41131, and can give a coated article beingexcellent in weather resistance and having a good appearance.

In an actual coating site of a powder coating, from the viewpoint ofproductivity, coating and baking of plural powder coatings are carriedout on one coating line, and operation of the line is changed over foreach powder coating.

However only by mixing of a small amount of the powder coatingcontaining a fluorine-containing resin to other resin powder coating,various defects arise on a coating film of the other resin. This is oneof the reasons why fluorine-containing resin-based powder coatings arenot spread on the market irrespective of excellent physical propertiesof a coating film thereof.

The present inventors have continued their studies to find out afluorine-containing resin powder coating composition which is lessaffected by mixing of other coating composition on a coating line andhave found that the above-mentioned defects attributes to miscibility ofa fluorine-containing resin with other resin and further that afluorine-containing copolymer featured by insolubility intetrahydrofuran (THF) can solve the above-mentioned problem. Thus thepresent invention was completed.

DISCLOSURE OF INVENTION

Namely the present invention relates to the thermosetting powder coatingcomposition characterized in that the composition comprises (A) afluorine-containing copolymer having crosslinkable functional group and(B) a curing agent and that the fluorine-containing copolymer (A) has aperfluoroolefin unit, has a fluorine content of not less than 10% byweight and is not dissolved in THF substantially.

It is preferable that the fluorine-containing copolymer (A) havingcrosslinkable functional group has a melting point of not more than 160°C. and a melt flow rate (MFR) of from 1 to 1,000 g/10 min when measuredat 130° C. at a load of 2.1 kg.

Examples of the preferred fluorine-containing copolymer (A) havingcrosslinkable functional group are those comprising tetrafluoroethylene(TFE), hexafluoropropylene (HFP), ethylene (ET) and monomer unit havingcrosslinkable functional group and being copolymerizable therewith orthose comprising TFE, HFP, isobutylene (IB) and monomer unit havingcrosslinkable functional group and being copolymerizable therewith.

Example of the preferred crosslinkable functional group is at least oneof hydroxyl, carboxyl and epoxy.

Further it is preferable to introduce a vinyl ester compound unit, forexample, vinyl benzoate unit and/or vinyl pivalate unit as a unitconstituting the copolymer (A).

The present invention also relates to a coated article obtained bycoating the above-mentioned thermosetting powder coating composition toa substrate and then baking it.

BEST MODE FOR CARRYING OUT THE INVENTION

First the fluorine-containing copolymer (A) having crosslinkablefunctional group and used in the present invention is explained below.

The fluorine-containing copolymer (A) having crosslinkable functionalgroup is one which has at least the following characteristics (1) to(4).

(1) Having a Perfluoroolefin Unit

Example of perfluoroolefin is, for instance, at least one ofperfluoroolefins such as TFE, HFP and perfluoro(vinyl ether).Particularly TFE and HFP are preferred. When the copolymer has aperfluoroolefin unit, a coating film being excellent in weatherresistance, water resistance and stain-proofing property can beobtained. It is preferable that the perfluoroolefin unit is contained inthe copolymer in an amount of not less than 5% by mole, especially 10 to95% by mole.

(2) Having a Fluorine Content of Not Less Than 10% by Weight

The fluorine content derives from the perfluoroolefin unit and/or otherfluorine-containing monomer. The fluorine content is not less than 10%by weight, preferably 20 to 75% by weight for the same reason as in (1)above.

Examples of the other fluorine-containing monomer are, for instance,vinylidene fluoride, trifluoroethylene, monofluoroethylene,chlorotrifluoroethylene, and the like. Those other fluorine-containingmonomer units are optional units. A content thereof is not more than 30%by mole, usually 0 to 10% by mole.

(3) Being Insoluble in THF Substantially

Being insoluble in THF means being inferior in compatibility with aresin soluble in THF. Namely when after coating of a powder coating of aresin soluble in THF, the powder coating of the present invention iscoated on the same coating line, or when carrying out coating in thereverse order, the fluorine-containing copolymer (A) is less affected byother resin, and the influence of mixing of the fluorine -containingcopolymer (A) on the other powder coating can be decreased.

Being insoluble substantially encompasses the case of being soluble inTHF in a concentration of less than 0.5% by weight. This is because whensubstantially measuring an intrinsic viscosity [η] of the resin in THFsolution, a reliable intrinsic viscosity [η] cannot be measured unlessthe copolymer has a solubility of about 0.5% by weight or more.

Examples of the resin which is soluble in THF and is used for a powdercoating are, for instance, an acrylic resin, polyester resin, epoxyresin, fluorine-containing resin described in JP-B-6-104792, and thelike.

(4) Having Crosslinkable Functional Group

The crosslinkable functional group has functions of giving a curing siteto the fluorine-containing copolymer (A) and giving a highly hardcoating film subjected to thermosetting by a reaction with a curingagent, thus increasing a surface hardness while maintaining goodflexibility.

In the present invention, examples of the crosslinkable functional groupare, for instance, functional groups represented by the formulae (i):

wherein R is an alkyl group having 1 to 3 carbon atoms.

Among the above-mentioned functional groups, preferred are thoserepresented by the formulae (ii):

Examples of the monomer capable of introducing such a functional groupare, for instance, perfluorobutenoic acid (PFBA), a fluorine-containingmonomer having an ether unit described in JP-A-8-67795 and in addition,non-fluorine-containing monomer having carboxyl such as maleic anhydride(MAL); hydroxyl-containing monomer such as hydroxybutyl vinyl ether(HBVE) and allyl alcohol; epoxy-containing monomer such as glycidylvinyl ether (GVE); vinylmethoxysilane, vinylethoxysilane, monomer havinghydrolyzable silyl group described in JP-A-8-120211, monomer havingaminopropoxy group, and the like.

From the viewpoint of reactivity in the baking temperature range in caseof combination use with a known curing agent, preferred are PFBA,carboxyl-containing monomer such as maleic anhydride,hydroxyl-containing monomer such as HBVE and glycidyl-containing monomersuch as GVE.

The crosslinkable functional group forms a curing site, and its amountvaries depending on reactivity of the functional group and kind of acuring agent. It is preferable that based on the wholefluorine-containing resin, an acid value is from 1 to 300 mgKOH/g, ahydroxyl value is from 1 to 200 mgKOH/g or an equivalent of epoxy isfrom 5 to 15,000 equivalents.

It is further preferable that the copolymer has the followingcharacteristics.

(5) Having a Melting Point of Not More Than 160° C.

When the melting point is in this range, a good flow characteristic isgiven at baking.

(6) MFR Being From 1 to 1,000 g/10 min when Measured at 130° C. at aLoad of 2.1 kg (The Measuring Conditions are Hereinafter the Same)

MFR is an important factor at melt-kneading or baking, particularly atbaking. The larger the MFR is, the more the flowing property of moltenresin increases. Therefore a smooth and uniform coating film is easilyformed. But on the other hand, dripping easily occurs, and at kneading,shearing is not applied to a kneaded composition and uniform kneading isdifficult. There occurs a defect that water resistance and impactresistance of a coating film are lowered. When the MFR is too small,flowability at baking is insufficient and a coating film does not becomesmooth and uniform. A preferred MFR is from 5 to 100 g/10 min.

From the above-mentioned points of view, a content of the unit givingcrosslinkable functional group may be selected in the range of from 0.1to 30% by mole, especially 1 to 20% by mole based on thefluorine-containing copolymer.

Also when the fluorine-containing copolymer (A) contains a vinyl estercompound unit as a constitutive unit thereof, adhesion of the obtainedcoating film to a substrate is enhanced, and also compatibility with acuring agent is improved, thus giving a coating film having a highgloss. Examples of the vinyl ester compound are non-fluorine-containingvinyl esters, for instance, vinyl benzoate (VBz), vinyl pivalate (VPi)and a mixture thereof. It is desirable that the vinyl ester compound isintroduced in the copolymer (A) in an amount of 0.1 to 25% by mole,preferably 0.5 to 20% by mole.

The fluorine-containing copolymer having crosslinkable functional groupcan be obtained by copolymerizing each of the above-mentioned monomers.The polymerization may be carried out by usual polymerization methodssuch as emulsion polymerization, suspension polymerization and solutionpolymerization. Also a monomer having crosslinkable functional group maybe grafted on the copolymer.

Non-restricted examples of the fluorine-containing copolymer havingcrosslinkable functional group of the present invention are those havingthe following combinations of monomers and satisfy the requirements (1)to (4) and further preferably (5) and (6).

(I) {circle around (1)} Perfluoroolefin not less than 5% by mole {circlearound (2)} Other fluorine-containing monomer  0 to 95% by mole {circlearound (3)} Other non-fluorine-containing monomer  0 to 95% by mole{circle around (4)} Crosslinkable functional not less than 0.1% by molegroup-containing monomer (II) {circle around (1)} At least one of TFEand HFP not less than 5% by mole {circle around (2)} Otherfluorine-containing monomer  0 to 95% by mole {circle around (3)}Non-fluorine-containing olefin  0 to 95% by mole {circle around (4)}Monomer containing functional not less than 0.1% by mole grouprepresented by the above-mentioned formula (i) (III) {circle around (1)}At least one of TFE and HFP not less than 10% by mole {circle around(2)} Other fluorine-containing monomer  0 to 20% by mole {circle around(3)} Non-fluorine-containing olefin 10 to 70% by mole {circle around(4)} Monomer containing functional group not less than 0.1% by molerepresented by the above-mentioned formula (i) (IV) {circle around (1)}At least one of TFE and HFP not less than 20% by mole {circle around(2)} Other fluorine-containing monomer  0 to 5% by mole {circle around(3)} Ethylene (ET) 20 to 50% by mole {circle around (4)} Monomercontaining functional group not less than 0.1% by mole represented bythe above-mentioned formula (ii) (V) {circle around (1)} At least one ofTFE and HFP not less than 20% by mole {circle around (2)} Otherfluorine-containing monomer  0 to 5% by mole {circle around (3)}Isobutylene (IB) 20 to 50% by mole {circle around (4)} Monomercontaining functional group not less than 0.1% by mole represented bythe above-mentioned formula (ii) (VI) {circle around (1)} At least oneof TFE and HFP not less than 10% by mole {circle around (2)} Otherfluorine-containing monomer  0 to 20% by mole {circle around (3)}Non-fluorine-containing olefin 10 to 70% by mole {circle around (4)}Monomer containing functional group not less than 0.1% by molerepresented by the above-mentioned formula (i) {circle around (5)} Vinylester compound  1 to 15% by mole (VII) {circle around (1)} At least oneof TFE and HFP not less than 20% by mole {circle around (2)} Otherfluorine-containing monomer  0 to 5% by mole {circle around (3)} Atleast one of ET and IB 20 to 50% by mole {circle around (4)} Monomercontaining functional group not less than 0.1% by mole represented bythe above-mentioned formula (ii) {circle around (5)} At least one of VBzand VPi  1 to 15% by mole

Non-restricted examples of more concrete copolymer are as follows.

TFE/HFP/ET/PFBA copolymer (mole ratio: 25 to 40/10 to 20/35 to 48/0.1 to10), TFE/HFP/ET/HBVE copolymer (mole ratio: 25 to 40/10 to 20/35 to48/0.1 to 10), TFE/HFP/ET/GVE copolymer (mole ratio: 25 to 40/10 to20/35 to 48/0.1 to 10), TFE/HFP/IB/HBVE copolymer (mole ratio: 25 to40/10 to 20/35 to 48/0.1 to 10), TFE/HFP/ET/HBVE/VBz copolymer (moleratio: 25 to 40/10 to 20/35 to 48/0.1 to 10/3 to 8),TFE/HFP/ET/HBVE/VBz/VPi copolymer (mole ratio: 25 to 40/10 to 20/35 to48/0.1 to 10/3 to 8/3 to 8)

TFE/HFP/ET copolymer described in JP-A-8-41131 does not have functionalgroup and does not satisfy the Requirement (4). A fluorine-containingcopolymer (JP-A-9-165535) mainly comprising vinylidene fluoride (VdF)does not satisfy insolubility in THF (Requirement (3)).

It is preferable that the fluorine-containing copolymer havingcrosslinkable functional group and used in the present invention furtherhas the following physical property.

Glass transition temperature (Tg): It is preferable that the glasstransition temperature is not more than 150° C., especially 40° to 120°C. (measured with DSC) from the viewpoint of giving a coating film beingexcellent in leveling property and appearance even at relatively lowbaking temperature.

The above-mentioned fluorine-containing copolymer having crosslinkablefunctional group not only gives excellent weather resistance, chemicalresistance and stain removable property to an obtained coating film butalso improves impact resistance and flexibility.

Then the curing agent which is another component of the thermosettingpowder coating composition of the present invention is explained below.

A curing agent to be used may be selected optionally depending on kindof the above-mentioned crosslinkable functional group, a melt-kneadingtemperature at making a coating, a baling temperature, etc. In formerthermosetting powder coating compositions containing afluorine-containing copolymer, selection of a curing agent was difficultfrom the viewpoint of its compatibility with the copolymer, and kind ofusable curing agent, particularly a combination with a resin waslimited. According to the present invention, since crosslinkablefunctional group is introduced into the above-mentionedfluorine-containing copolymer, kind and combination of usable curingagent can be extended.

Examples of the usable curing agent are, for instance, epoxy or glycidylcompounds such as alicyclic epoxy resin, GMA acryl, aliphatic oxysilane,triglycidyl isocyanurate (TGIC), diglycidyl terephthalate, diglycidylp-hydroxybenzoate, spiroglycol diglycidylether and hydantoin compounds;isophorone diisocyanate, tolylene diisocyanate, xylilene diisocyanate,4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, dimersthereof and blocked isocyanates obtained by blocking an isocyanate groupof alcohol-modified polyisocyanate with a blocking agent (for example,ε-caprolactam, phenol, benzyl alcohol, methyl ethyl ketone oxime, etc.);polybasic acid curing agent such as β-hydroxyalkylamide; polycarboxylicacids, e.g. aliphatic dibasic acids such as fumaric acid, succinic acid,adipic acid, azelaic acid, sebacic acid and dodecandioic acid (DDA) andacid anhydrides such as phthalic anhydride, trimellitic anhydride andpyromellitic anhydride; tetramethoxymethylglycoluryl, isocyanate-modified silane coupling agent, and other curing agents described inJP-B-6-104792, JP-A-7-188587 and JP-A-1-103670.

Among them, particularly from the viewpoint of compatibility with thecrosslinkable functional group in the fluorine-containing copolymer (A),preferred combinations are as follows.

(1) Crosslinkable functional group: Hydroxyl group Curing agent: Blockedisocyanate, polyurethodione

(2) Crosslinkable functional group: Carboxyl group Curing agent:Triglycidyl isocyanurate, β-hydroxyalkylamide, GMA acryl

(3) Crosslinkable functional group: Glycidyl group Curing agent:Aliphatic dibasic acid

It is preferable that an amount of the curing agent is from 0.1 to 1.2equivalents, especially 0.5 to 1.0 equivalent to an amount of functionalgroup contained in the fluorine-containing copolymer (A). When less than0.1 equivalent, an effect of improvement by crosslinking in crackresistance at bending and impact resistance is not sufficient and waterresistance is also lowered. When more than 1.2 equivalents, it resultsin lowering of appearance of a coating film.

In addition to the curing agent, a curing catalyst may be blended.Examples of the curing catalyst are, for instance, quaternary ammoniumsalts such as tetrabutylammonium chloride, tetrabutylammonium bromideand tetrabutylammonium iodide; quaternary phosphonium salts such asethyltriphenylphosphonium acetate; phosphines such astriphenylphosphine; imidazoles such as 2-methylimidazole; organotincompounds such as dibutyltindilaurate and stannous octanoate;methyltolylsulfoneimide and stannous methanesulfonate, and the like. Thecuring catalyst may be blended in an amount of from about 0.1 part (partby weight, hereinafter the same) to about 3 parts to 100 parts of thefluorine-containing copolymer (A).

In addition to those additives, to the powder coating composition of thepresent invention may be blended various additives usually added in thefield of paints, in an amount not lowering an effect of the presentinvention. Examples of such other additives are a pigment, extendedpigment, flow control agent, antioxidant, thermal deteriorationpreventive agent, ultraviolet ray absorber, foaming inhibiting agent,flatting control agent, defoaming agent, electric charge control agent,antistatic agent, and the like.

Since a coating film formed with the fluorine-containing copolymer (A)of the present invention is transparent, various kinds of pigments canbe used. For example, there are organic pigments such as condensed azocompounds, isoindolinone, quinacridone, diketopyrrolopyrol,anthraquinone, dioxazine and various organometal complexes; inorganicpigments such as titanium oxide (Preferred are one having rutile-typestructure, and further preferable are alumina-treated, silica-treated orzirconia-treated titanium oxides), red iron oxide, yellow iron oxide,black iron oxide, carbon, chromium oxide, lead chromate, white lead andmolybdenum orange; metal powders such as aluminum powder and stainlesssteel powder; and the like. Among them, inorganic pigments are preferredfrom the viewpoint of weather resistance which is one of the features ofthe present invention, particularly to maintain a gloss retention ratioand inhibit fading of color. A preferred content of the pigment is notmore than 80 parts on the basis of 100 parts of the resin.

Examples of the extended pigment are, for instance, talc, silica,calcium carbonate, barium sulfate, mica, diatomaceous silica, asbestos,basic silicate, and the like.

Examples of the flow control agent are, for instance, acrylate polymerssuch as polylauryl acrylate, polybutyl acrylate and poly-2-ethylexylacrylate; ester of polyethylene glycol and perfluorocarboxylic acid andfluorine-containing polymers having a low melting point such asVdF/TFE/HFP copolymer (excluding VdF polymers having crosslinkablefunctional group); silicone polymers such as polydimethylsiloxane andpolymethylphenylsiloxane; and the like.

Then the process for preparing the powder coating composition of thepresent invention is explained below. As mentioned above, one of thefeatures of the composition of the present invention is such thatcoating defects attributable to contamination are hard to arise whenchanging to or from a powder coating of other resin on a powder coatingline.

The preparation process comprises the basic steps such as apre-pulverizing step, dry blending step, melt-kneading step, pulverizingstep and classifying step. (Pre-pulverizing step)

As mentioned above, the fluorine-containing copolymer havingcrosslinkable functional group can be obtained in various forms such aspowder, flake, bulk, and the like. In order to obtain good mixing in thefollowing dry blending step, the copolymers are formed into pellets ofnot more than 5 mm or pulverized into an average particle size of about50 μm to about 100 μm. (Dry blending step)

The fluorine-containing copolymer having crosslinkable functional groupin the form of powder or pellet, curing agent, curing catalyst andadditives such as a pigment are dry-blended. A mixer to be used isusually a high speed mixer, low speed mixer or Henschel mixer. If atemperature inside the mixer is elevated too high, a reaction of thecrosslinkable functional group with the curing agent advances. Thereforeit is preferable that the inside temperature is maintained at atemperature of not more than 80° C. by controlling time and mixertemperature.

Melt-kneading Step

The above-mentioned dry-blended product is put in a melt-kneader, meltedat a temperature of not less than a melting point or Tg of thefluorine-containing copolymer (A) to knead sufficiently, and thenextruded in the form of sheet. In that case, an extruder which is highin productivity in continuous production is used preferably. Examples ofusual melt-kneader are a single screw extruding kneader, two screwextruding kneader, heating kneader and heating roll. A melt-kneadingtemperature and time are 80° to 120° C. and usually several tens ofseconds, respectively so that the reaction of the functional group inthe resin and the curing agent does not advance too much.

Pulverizing Step

The sheet melt-extruded in a specified form is, after cooling andsolidifying, roughly pulverized into chips of about 5 mm to about 15 mmand then finely pulverized. In that case, it is preferable that thepulverizer is maintained at a constant temperature with very lowtemperature pulverizing, air-cooling or water-cooling means. As thepulverizer, a high speed impact pulverizer, high speed pin typepulverizer, or the like is used preferably.

Classifying Step

The finely pulverized powder is classified with a centrifugalclassifier, blower type sieving machine, sieve shaking machine, or thelike. A narrow particle size distribution is preferable. It ispreferable that an average particle size of the powder coatingcomposition is from 1 to 100 μm, especially 10 to 50 μm. When less than1 μm it is difficult to control a coating thickness because theparticles are subject to electrostatic repulsion, and there occurproblems with lowering of a coating efficiency due to lowering ofcollecting efficiency with a cyclone in case of recycling and alsolowering of safety workability due to permeation through a protectionmask. When more than 100 μm, leveling property is lowered, therebycausing problems that appearance of a coating film becomes poor andcoating thin cannot be carried out. An average particle size isdetermined by a desired coating thickness. For example, in case of acoating thickness of about 40 μm to about 50 μm, the average particlesize is preferably 25 to 30 μm. The smaller the average particle sizeis, the more the appearance of coating film is enhanced, and coatingthin is possible, but a blockage occurs at spray-coating, therebycausing lowering of workability and adhesion of a coating.

The thermosetting powder coating composition of the present inventioncan be prepared in such a manner mentioned above.

The thermosetting powder coating composition of the present inventioncan be coated on various substrates by known applying methods. Then thecoating film obtained by baking the coated film is excellent in itsappearance such as smoothness and gloss, surface hardness, mechanicalproperties such as flexibility and impact resistance, adhesion to asubstrate, weather resistance, stain-proofing property and waterresistance.

Namely the present invention relates to the coated article obtained bycoating the above-mentioned thermosetting powder coating composition ona substrate and then baking it for curing.

For coating, known coating methods can be employed. For example, thereare electrostatic powder spray coating method, fluid bed coating method,electrostatic dip coating method, and the like. A coating thickness isusually in the range of from 20 to 100 μm.

Then the coating film is baked. A baking temperature is not more than200° C., usually not less than 150° C., preferably 160° to 200° C. Abaking time is from 10 to 30 minutes, usually 15 to 20 minutes. At thatbaking temperature, the powder coating composition of the presentinvention exhibits excellent flowability and gives a smooth and uniformbaked coating film.

The powder coating composition of the present invention is alsoexcellent in adhesion to a substrate. The preferable substrate is onewhich has electric conductivity to enable electrostatic coating.Examples thereof are, for instance, various metal plates such asstainless steel plate, aluminum plate, steel plate and galvanized steelplate, and in addition, heat resistant engineering plastics such aspolycarbonate, polyphenylene oxide, polyethylene terephthalate,polyether sulfone, polyamideimide and polyether ether ketone which areendowed with electric conductivity by dispersing a conductive carbontherein. It is preferable that those substrates are subjected to removalof rust by sand blasting or acid washing, baking, degreasing by washingwith a solvent, with emulsion type cleaner or alkali, phosphating withzinc phosphate, calcium phosphate or iron phosphate, or chemicalconversion treatment such as chromate treatment, alumite treatment orchromium phosphate treatment. In that case, though the coatingcomposition of the present invention has enough adhesion to thosesubstrates even in case of a single use thereof, as case demands, it ispossible to carry out intermediate coating of zinc rich rust-preventiveprimer or various primers such as an epoxy resin and acrylic resintogether. The intermediate coating may be applied in any form of solventtype coating, aqueous coating, powder coating or the like. It ispreferable to apply in the form of powder coating from the viewpoint ofworkability in the present invention.

The coated article of the present invention is used for variousapplications. Non-restricted examples of the application are, forinstance, applications described in “Handbook of Powder CoatingTechnique” edited by Nippon Funtai Toso Kogyo Kyokai (1994), pp 169 to173 such as construction and building material, electric communicationdevice, vehicles, road materials, water and gas service materials, metalproducts, domestic appliances, machines, tools, measuring instruments,medical instruments, utensils for maintenance, agricultural materials,ships, sports and leisure products, and the like.

Then the present invention is explained by means of examples, but is notlimited to them.

Preparation Example 1

A 4-liter pressure resistant reactor equipped with a stirrer was chargedwith 1,000 ml of deionized water, and feeding of pressurized nitrogenand deairing were repeated to remove dissolved oxygen. Then the reactorwas charged with 407 g of chlorofluoroethane (HCFC-141b), 15 g ofperfluorobutenoic acid (PFBA) and 794 g of hexafluoropropane (HFP)successively. A pressure inside the reactor was increased up to 12kgf/cm² at 35° C. with a monomer mixture of tetrafluoroethylene(TFE)/ethylene (ET) in a % by mole ratio of 82/18. Then the reactor wascharged with 4 g of cyclohexane and 48 g of 25% flon 225 solution ofisobutyryl peroxide, and the above-mentioned monomer mixture wassupplied continuously so that the inside pressure became constant at 12kgf/cm². Every three hours after starting of the reaction, 8 g of 25%flon 225 solution of isobutyryl peroxide and 3 g of PFBA were addedthree times. After 12-hour reaction, the inside of the reactor wasrestored to normal temperature and normal pressure to terminate thereaction. After the obtained solid was washed and dehydrated, it wasvacuum-dried at 80° C. to give 133 g of TFE/HFP/ET/PFBA copolymer (whitepowder). Components, melting point (Tm), glass transition temperature(Tg), MFR and solubility in THF of the obtained copolymer were measuredby the methods mentioned below. Melting point, glass transitiontemperature: A heat balance of 10 mg of VdF polymer was measured at aheat-up speed of 10° C./min in a temperature range of −25° C. to 200° C.by using Thermal Analysis System (available from Perkin Elmer Co.,Ltd.), and a top peak was assumed to be a melting point. Since the glasstransition temperature (Tg) was detected as two variable polar points,it was obtained by a center point method.

MFR: Measurement was carried out under the conditions of 130° C., a loadof 2.1 kg and 10 minutes. In case of much flow, a period of time inwhich 20 g of resin flowed was measured and converted to an amount ofresin flowing for 10 minutes.

Solubility in THF: 0.5 Gram of resin in the form of powder was put in 10ml of THF at room temperature, and after allowed to stand for 72 hours,dissolving state was observed with naked eyes.

The results are shown in Table 1.

Preparation Examples 2 to 8 and Comparative Preparation Examples 1 to 2

Polymerization was carried out in the same manner as in PreparationExample 1 except that monomers, amount of cyclohexane and polymerizationtime were changed as shown in Table 1. The same measurements as inPreparation Example 1 were carried out with respect to the obtainedfluorine-containing copolymer. The results are shown in Table 1.

TABLE 1 Prep. Ex. Com. Prep. Ex. 1 2 3 4 5 6 7 8 1 2 Monomer componentsTFE/ET (% by 82/18 82/18 82/18 82/18 82/18 — 82/18 82/18 82/18 76/24mole ratio) TFE/IB (% by — — — — — 82/18 — — — — mole ratio) HFP (g) 794794 794 794 794 794 794 794 794 900 PFBA (g) 24 24 — — — — — — — — HBVE(g) — — 21 — 21 21 21 21 — — GVE (g) — — 21 — — — — — — VBz (g) — — — —— — 10 10 — — VPi (g) — — — — — — — 10 — — Amount of 4 4 2 2 10 1 2 1 44 cyclohexane (g) Polymerization 12 12 12 12 24 12 15 18 12 12 time (hr)Obtained weight 133 165 142 146 36 130 130 90 178 125 (g) Components ofpolymer TFE 35 33 31 34 33 30 30 31 35 32 HFP 16 18 18 17 18 17 17 16 1820 ET 45 45 48 44 45 — 44 42 47 48 IB — — — — — 49 — — — — PFBA 4 4 — —— — — — — — HBVE — — 3 — 4 4 4 3 — — GVE — — — 5 — — — — — — VBz — — — —— — 5 5 — — Vpi — — — — — — — 3 — — Melting point 151 123 123 118 118 85110 105 120 132 (° C.) Glass transition 51 42 38 35 38 33 35 35 53 65temperature (° C.) MFR (g/10 min) 2 67 56 42 823 550 85 150 73 0.5Solubility in Insoluble Insoluble Insoluble Insoluble InsolubleInsoluble Insoluble Insoluble Insoluble Insoluble THF Abbreviations inTable 1 represent the following compounds. TFE: Tetrafluoroethylene HFP:Hexafluoropropylene ET: Ethylene IB: Isobutylene PFBA: Perfluorobutenoicacid HBVE: Hydroxybutyl vinyl ether GVE: Glycidyl vinyl ether VBz: Vinylbenzoate VPi: Vinyl pivalate

Comparative Preparation Example 3

A 1-liter pressure resistant reactor was charged with 523 g of t-butanol(t-BA), 53 g of cyclohexyl vinyl ether (CHVE), 30 g of isobutyl vinylether (IBVE), 83 g of hydroxybutyl vinyl ether (HBVE), 3.3 g ofpotassium carbonate and 0.23 g of azobisisobutylonitrile, followed bysolidifying with liquid nitrogen and deairing to remove dissolvedoxygen. After that, 167 g of pressurized CTFE was introduced and thereactor was heated up to continue a reaction at 65° C. over 10 hours.Then after cooling, residual monomer was distilled off, a solution wascollected and a dispersion medium was distilled off at 60° C. underreduced pressure to give a resin. This resin dissolved in THF. A glasstransition temperature and MFR thereof were 24° C. and 116,respectively.

EXAMPLE 1

100 Gram of fluorine-containing copolymer having crosslinkablefunctional group which was obtained in Preparation Example 1, 4 g oftriglycidyl isocyanurate (TGIC available from Rhom & Haas Co., Ltd.), 15g of titanium oxide, 0.5 g of flowability control agent (MODAFLOWavailable from Monsanto Chemical Co., Ltd.) and 0.5 g of benzoin weredry-blended at 25° C. for 15 minutes with Henschel mixer to give auniform mixture. The mixture was melt-kneaded at 100° C. for one minutewith Buss Co-kneader (available from Buss Co., Ltd.), extruded into asheet and then pelletized. Then 20 g of pellets was pulverized at roomtemperature (about 20° C.) for five minutes with Micro Hammer Mill(available from IKA Co., Ltd.). The obtained powder was passed through a200 mesh screen for classification to give a powder coating compositionhaving an average particle size of 50 μm.

EXAMPLES 2 to 8 and Comparative Examples 1 to 3

Powder coating compositions were obtained in the same manner as inExample 1 except that fluorine-containing copolymer and curing agentwere changed as shown in Table 2.

With respect to those powder coating compositions, an effect of aremaining other resin on the composition was determined in the mannermentioned below.

To 100 g each of the powder coating compositions of Examples 1 to 8 andComparative Examples 1 to 3, was mixed 0.5 g of polyester resin powder(FINEDIC M-8026 available from Dai-Nippon Ink Co., Ltd.) having anaverage particle size of 50 μm. Then the compositions were coated on a0.3 mm thick JIS 2003 A 714 chemical conversion-treated aluminum sheetat an applied voltage of 60 kV with a corona discharge type powdercoating gun (GX3300 available from Onoda Cement Kabushiki Kaisha), andthen immediately baked at 180° C. for 20 minutes to give a coatedarticle.

Appearance of the coated article was observed with naked eyes. Theresults are shown in Table 2.

TABLE 2 Example Comparative Example 1 2 3 4 5 6 7 8 1 2 3 Fluorine-Prep. Prep. Prep. Prep. Prep. Prep. Prep. Prep. Com. Prep. Com. Prep.Com. Prep. containing Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8Ex. 1 Ex. 2 Ex. 3 resin (g) (100) (100) (100) (100) (100) (100) (100)(100) (100) (100) (100) Curing agent TGIC TGIC B-NCO DDA B-NCO B-NCOB-NCO B-NCO — — B-NCO (g) (4) (4) (7.5) (7.5) (7.5) (7.5) (7.5) (7.5)(—) (—) (13) Effect of remaining Good Good Good Good Good Good Good GoddGood Occurrence Occurrence other resin appear- appear- appear- appear-appear- appear- appear- appear- appearance of nibs of cissing ance anceance ance ance ance ance ance Abbreviations in Table TGIC: Triglycidylisocyanurate B-NCO: Blocked isocyanate DDA: Dodecyldioic acid

EXAMPLES 9 to 16 and Comparative Examples 4 to 6

The powder coating compositions shown in Table 3 were coated on a 0.3 mmthick JIS 2003 A 714 chemical conversion-treated aluminum sheet at anapplied voltage of 60 kV with a corona discharge type powder coating gun(GX3300 available from Onoda Cement Kabushiki Kaisha), and thenimmediately baked at 180° C. for 20 minutes to give a coated article.

The following characteristics of the coated article were determined. Theresults are shown in Table 3.

Thickness of Coating Film

Coating thickness is measured with an eddy-current instrument EL10D formeasuring a coating thickness (available from Kabushiki Kaisha SankoDenshi Kenkyusho).

Appearance of Coating Film

Fluorescent light is emitted to the coated article and a shape of thelight reflected on the surface of the coating film is evaluated withnaked eyes.

A: There is no deformation on the shape of light.

B: There is a deformation slightly on the shape of light.

C: There is a deformation greatly on the shape of light.

Gloss

A specular gloss at an angle of 60 degrees is measured according to JISK 5400-6.7.

Pencil Hardness

A pencil hardness is measured according to JIS K 5400.

Impact Resistance

After carrying out a falling ball impact test according to AAMA605,peeling test is conducted and impact resistance is evaluated under thefollowing criteria.

◯: There is neither cracking nor peeling on the coating film.

x : Cracking and peeling are found on the coating film.

Flexibility

A bending test is carried out according to AAMA605.

Adhesion

A cross cut test for adhesion is carried out according to AAMA605.

Boiling Water Resistance

After a test of dipping in boiling water according to AAMA605, adhesionis evaluated.

Stain-proofing Property

An oily ink (red) is applied to the coated plate, and after allowed tostand at room temperature for 24 hours, is wiped off with a clothimpregnated with ethanol. Stain-proofness is evaluated with a colordifference AE before and after the test under the following criteria.

A: ΔE is less than 1.

B: ΔE is not less than 1 and less than 5.

C: ΔE is not less than 5.

Weather Resistance

A gloss retention is measured after a lapse of 2,000 hours by using anaccelerated weather resistance tester (sunshine weather-o-meter).

TABLE 3 Example Comparative Example 9 10 11 12 13 14 15 16 4 5 6 Powdercoating composition Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Com.Ex. 1 Com. Ex. 2 Com. Ex. 3 Thickness of coating 40 40 40 40 40 40 40 4040 40 40 film (μm) Appearance of coating film A A A A A A A A A A AGloss 58 72 75 77 78 75 80 84 78 65 78 Pencil hardness 2H 2H H 2H H H 2H2H 2B 2B HB Impact resistance ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Flexibility 1T 1T 1T1T 2T 1T 1T 1T 1T 1T 3T Adhesion 100/100 100/100 100/100 100/100 100/100100/100 100/100 100/100 100/100 100/100 100/100 Boiling water resistance100/100 100/100 100/100 100/100 100/100 100/100 100/100 100/100 100/100100/100 100/100 Stain-proofing property A A A A A A A A A A B Weatherresistance 98 98 98 97 78 97 98 98 87 85 93

INDUSTRIAL APPLICABILITY

When the powder coating composition of the present invention is used, acoating line can be shared with other powder coating composition, andyet a coated article having a coating film excellent in physicalproperties can be provided.

What is claimed is:
 1. A thermosetting powder coating composition,characterized in that the composition comprises (A) afluorine-containing copolymer having crosslinkable functional group and(B) a curing agent and that the fluorine-containing copolymer (A) has aperfluoroolefin unit, has a fluorine content of not less than 10% byweight and is not dissolved in tetrahydrofuran substantially.
 2. Thethermosetting powder coating composition of claim 1, wherein a meltingpoint of the fluorine-containing copolymer (A) having crosslinkablefunctional group is not more than 160° C.
 3. The thermosetting powdercoating composition of claim 1, wherein a melt flow rate of thefluorine-containing copolymer (A) having crosslinkable functional groupis from 1 to 1,000 g/10 min when measured at 130° C. at a load of 2.1kg.
 4. The thermosetting powder coating composition of claim 3, whereinthe fluorine-containing copolymer (A) having crosslinkable functiongroup is a copolymer comprising tetrafluoroethylene,hexafluoropropylene, ethylene and monomer having crosslinkablefunctional group and being copolymerizable therewith.
 5. Thethermosetting powder coating composition of claim 3, wherein thefluorine-containing copolymer (A) having crosslinkable functional groupis a copolymer comprising tetrafluoroethylene, hexafluoropropylene,isobutylene and monomer having crosslinkable functional group and beingcopolymerizable therewith.
 6. The thermosetting powder coatingcomposition of claim 3, wherein the crosslinkable functional group is atleast one of hydroxyl, carboxyl and epoxy.
 7. The thermosetting powdercoating composition of claim 3, wherein the fluorine-containingcopolymer (A) further contains a vinyl ester compound unit.
 8. Thethermosetting powder coating composition of claim 7, wherein the vinylester compound unit is a vinyl benzoate unit and/or a vinyl pivalateunit.
 9. A coated article obtained by coating the thermosetting powdercoating composition of claim 3 to a substrate and then baking it. 10.The thermosetting powder coating composition of claim 4, wherein thecrosslinkable functional group is at least one of hydroxyl, carboxyl andepoxy.
 11. The thermosetting powder coating composition of claim 5,wherein the crosslinkable functional group is at least one of hydroxyl,carboxyl and epoxy.
 12. The thermosetting powder coating composition ofclaim 4, wherein the fluorine-containing copolymer (A) further containsa vinyl ester compound unit.
 13. The thermosetting powder coatingcomposition of claim 5, wherein the fluorine-containing copolymer (A)further contains a vinyl ester compound unit.
 14. The thermosettingpowder coating composition of claim 6, wherein the fluorine-containingcopolymer (A) further contains a vinyl ester compound unit.
 15. Thethermosetting powder coating composition of claim 12, wherein the vinylester compound unit is a vinyl benzoate unit and/or a vinyl pivalateunit.
 16. The thermosetting powder coating composition of claim 13,wherein the vinyl ester compound unit is a vinyl benzoate unit and/or avinyl pivalate unit.
 17. The thermosetting powder coating composition ofclaim 14, wherein the vinyl ester compound unit is a vinyl benzoate unitand/or a vinyl pivalate unit.
 18. A coated article obtained by coatingthe thermosetting powder coating composition of claim 4 to a substrateand then baking it.
 19. A coated article obtained by coating thethermosetting powder coating composition of claim 5 to a substrate andthen baking it.
 20. A coated article obtained by coating thethermosetting powder coating composition of claim 6 to a substrate andthen baking it.
 21. A method for powder coating of substrates utilizinga single coating line, which comprises powder coating first substrateswith a first powder coating composition followed by baking and powdercoating second substrates with a second powder coating compositionfollowed by baking, said powder coating of first substrates and saidpowder coating of second substrates being carried out on the samecoating line, either sequentially or in reverse order, wherein one ofsaid first and second powder coating compositions is a thermosettingpowder coating composition as claimed in claim 1 and wherein the otherof said first and second powder coating compositions is soluble in THF.